Power train control system

ABSTRACT

A control system is shown for a multispeed forward and reverse track-laying vehicle power train, the control system having a manual forward and reverse control for effecting manual shifts between forward and reverse, a manual drive range control and an automatic drive range shifting operation and a steering control for effecting steering operation. The manual forward and reverse control provides selection between forward and reverse drive in the lowest drive range and prevents such shifting by the operator in all of the higher drive ranges. The manual drive range control provides selection between the drive ranges with the selected drive range being established immediately on an upshift and by speed governed automatic shifting operation on a downshift. The automatic drive range control provides automatic shifting using separate speed controlled upshift biases, an engine torque demand controlled upshift inhibiting bias and an engine torque demand controlled downshift bias. Both the manual forward and reverse control and the manual drive range control are electrically activated and in the event there is an interruption in electrical power, the directional drive selected by the manual forward and reverse control is maintained while the range control, if under manual control is automatically conditioned for automatic control to maintain power train control. A sequence control is effective to disengage the range drive to the load in the lowest drive range during shifting between forward and reverse to provide for engagement of the directional drive under no-load conditions. The steer control operates on a hydrostatic unit to control steering by controlling hydrostatic pump displacement while assuring straight vehicle no-drift motion when there is no steer demand. The controlling force effecting this pump displacement control is varied according to hydrostatic pump output to meet the varying steer load demands in both directions of steer. There is also provided a stroke or pump displacement limiter for limiting pump displacement regardless of the steer demanded by the operator to prevent pump overload. Hydrostatic system pressure is controlled by a pressure relief control in accordance with engine torque demand and vehicle speed to both prevent overloading of the hydrostatic pump and limit the degree of steer bias. The steer control signals the range control to inhibit automatic range shifting during steering operation. The hydrodynamic torque converter in the power train has a lockup drive which is normally disengaged on range shifting and is held engaged during low speed operation in each range to provide for utilization of vehicle momentum to provide power for steering while preventing engine stall.

United States Patent Schaefer [54] POWER TRAIN CONTROL SYSTEM [72]Inventor: Robert H.Schaefer,\Vestfield,lnd.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Aug. 3, 1970 21 Appl.No.: 60,453

Related U.S. Application Data [62] Division of Ser. No. 779,502, Nov.27, 1968,

Pat. No. 3,640,157.

Primary Examiner-Benjamin Hersh Assistant ExaminerJohn A. PekarAttorney-E. W. Christen, A. M. Heiter and R. L. Phillips [57] ABSTRACT Acontrol system is shown for a multispeed forward and reversetrack-laying vehicle power train, the control system having a manualforward and reverse control for efi'ecting manual shifts between forwardand reverse, a manual drive 'range control and an automatic drive rangeshifting operation and a steering control for effecting steeringoperation. The manual forward and reverse control provides selectionbetween forward and reverse drive in the lowest drive [4 1 Aug. 29,1972

7 range and prevents such shifting by the operator in all of the higherdrive ranges. The manual drive range control provides selection betweenthe drive ranges with the selected drive range being establishedimmediately on an upshift and by speed governed automatic shiftingoperation on a downshift. The automatic drive range control providesautomatic shifting using separate speed controlled upshift biases, anengine torque demand controlled upshift inhibiting bias and an enginetorque demand controlled downshift bias. Both the manual forward andreverse control and the manual drive range control are electricallyactivated and in the event there is an interruption in electrical power,the directional drive selected by the manual forward and reverse controlis maintained while the range control, if under manual control isautomatically conditioned for automatic control to maintain power traincontrol. A sequence control is effective to disengage the range drive tothe load in the lowest drive range during shifting between forward andreverse to provide for engagement of the directional drive under no-loadconditions. The steer control operates on a hydrostatic unit to controlsteering by controlling hydrostatic pump displacement while assuringstraight vehicle no-drift motion when there is no steer demand. Thecontrolling force effecting this pump displacement control is variedaccording to hydrostatic pump output to meet the varying steer loaddemands in both directions of steer. There is also provided a stroke orpump displacement limiter for limiting pump displacement regardless ofthe steer demanded by the operator to prevent pump overload. Hydrostaticsystem pressure is controlled by a pressure relief control in accordancewith engine torque demand and vehicle speed to both prevent overloadingof the hydrostatic pump and limit the degree of steer bias. The steercontrol signals the range control to inhibit automatic range shiftingduring steering operation. The hydrodynamic torque converter in thepower train has a lockup drive which is normally disengaged on rangeshifting and is held engaged during low speed operation in each range toprovide for utilization of vehicle momentum to provide power forsteering while preventing engine stall.

5Claims,9DrawingFigures United States Patent [151 3,687,210 Schaefer v I51 Aug. 29,1972

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SHEET 6 or 6 TRANSM|SS|ON SOLENOID VALVE RANGE 774 952 9|8 803 798 m;715 AUTOMATIC x F o 4 X X R 5 x x x X 2 x x g X X TEUTRAL x x RAUTOMATIC X 5 E 4 X x El 3 X X x INVENTOR. R 2 x x Yak/f hf Sa /ask! S lX X BY E NEUTRAL X x af ATTORNEY POWER TRAIN 'CQNTRQL SYSTEM Thisapplication is a division of application Ser. No. 779,502, filed Nov.27, 1968, now US. Pat. No. 3,640,157.

The invention herein described was made in the course of work under acontract or subcontract thereunder with the Department of Defense.

This invention relates to power train or transmission control systemsand more particularly to a control system for a track-laying vehiclepower train providing manual shift control, automatic shift control andsteering control.

The control system according to the present invention may be employed intrack-laying vehicle power trains or transmissions of the type shown inUS. Pat. No. 3,373,636 issued Mar. 19, 1968, to Livezey et al. andentitled VEHICLE TRANSMISSION INCLUD- ING STEERlNG BY DRlVlNG. Thecontrol system includes an upstream and a downstream main pressureregulator valve, the former regulating pressure at a value modulatedaccording to both drive range and torque converter operation and usedprimarily for drive range engagement and converter lockup and the latterregulating pressure at an unmodulated value used primarily fordirectional drive engagement, control functions and as a source forcontrol pressures. Two fluid velocity governors are provided, oneproducing a governor pressure ((31) proportional to converter turbineand power train output speed and the other producing a governor pressure(G2) which is zero throughout the lowest drive range and proportional torange unit and power train output speed in all of the higher driveranges. A pair of throttle pressure regulator valves provide threecontrol pressures, two of these control pressures (T and TV) derived byone valve from the unmodulated main pressure and the remaining controlpressure (range TV) derived by the other valve from the unmodulated mainpressure and TV pressure. The TV pressure is proportional to enginethrottle opening, T pressure is the upper portion of the TV pressurerange, and range TV pressure has a predetermined minimum value and isotherwise equivalent to TV pressure. A lockup valve under the control ofimplementing G1 pressure and inhibiting T and TV pressure determinesconverter lockup with a flow valve normally interrupting lockup duringrange shifting and a flow valve modulator valve under the control of TVpressure overriding the normal flow valve operation to permitmaintenance of lockup with G1 pressure during range downshifting below apredetermined TV pressure or part engine throttle opening. A neutralshift valve under the control of a manually controlled solenoid valvedetermines the delivery of the modulated main pressure to seriesarranged range shift valves for drive range engagement.

The range shift valves operate to automatically shift between the driveranges under the control of an upshift bias by 61 pressure for thelowest upshift, an upshift bias by G2 pressure for the higher upshifts,an upshift inhibiting bias by range TV pressure and a downstream bias byT pressure. The range shift valves under the control of manuallycontrolled solenoid valves provide for manual range selection. Formanual range selection, a manual signal valve under the control ofmanually controlled solenoid valves substitutes unmodulated mainpressure for the T pressure downshift bias on the proper range shiftvalves to provide automatic downshifting from any higher drive rangethrough any intermediate drive range to the manually selected driverange. This automatic downshifting with manual drive range selection iscontrolled to occur at a vehicle speed suitable for each lower driverange as determined by governor pressure bias, upshifts by manualselection occurring immediately.

A forward and reverse shift valve under the control of manuallycontrolled solenoid valves determines the delivery of unmodulated mainpressure for directional drive engagement in the selection being betweenforward and reverse drive. A forward and reverse inhibitor valve underthe control of G2 pressure permits shifts between forward and reverse inthe lowest drive range and prevents such shifting in all of the higherdrive ranges. A sequence valve under the control of the operation of theforward and reverse shift valve effects disengagement of the drive tothe load during a directional change in the lowest drive range to permitengagement of the directional drive under no-load conditions. Anautomatic shift inhibitor valve under the control of a steer signalpressure from the steer control inhibits automatic shifting duringsteering operation. There is also provided in the control system aconverter pressure regulator valve which limits pressure to the torqueconverter, this pressure being modulated in accordance with converteroperation, and an air valve which controls delivery of fluid tohydrodynamic and hydromechanical output brakes.

All of the solenoid valves are controlled by the operator from aselector box with a forward and reverse shift lever controlling solenoidvalve operation for directional change and the remaining solenoid valvescontrolled by a manual and automatic shift lever for both manual driveselection and automatic range shifting. The solenoid valves areconnected in the control system such that when they are allde-energized, the control system is conditioned for automatic rangeshifting in either drive direction, the forward and reverse shift valvebeing mechanically detented in each of its two drive determiningpositions. For automatic shifting operation, the forward and reverseshift lever is controlled by the operator to select the drive directiondesired by energization of the proper direction control solenoid valvewhile the manual and automatic shift lever is operated to de-energizethe remaining solenoid valves. Manual drive range selection is made byoperating the manual and automatic shift lever to energize the propersolenoid valves to establish the desired drive range while the forwardand reverse lever is operated to determine drive direction. Thus, withthis arrangement and in the event there is an interruption in theelectrical power while operating with manual drive selection, thecontrol system will be automatically conditioned for automatic rangeshifting in the direction previously determined so that range shiftingremains available.

The steer bias of the power train is effected by a converter pump drivenhydrostatic unit, hydrostatic pump displacement being controlled bysteer controls in the control system to control the steer bias. Amanually controlled steer valve controls the delivery of a controlpressure to vary hydrostatic pump displacement, the steer valveproviding pump displacement in proportion to manual steer input. Acentering and steer signal device accurately positions the steer valvefor zero pump displacement and thus no steer bias when a steer is notbeing demanded and supplies the steer signal pressure to the automaticshift inhibitor valve for inhibiting automatic shifting during steeringoperation. A control pressure regulator valve always responsive tohydrostatic pump output pressure modulates the control pressurecontrolling pump displacement so that it increases with increasinghydrostatic pump output pressure and thus steer effort. An overloadstroke limiter valve under the control of the pressure differentialacross the hydrostatic pump overrides steer control to prevent steerbias which would overload the hydrostatic pump. A relief valve is alwaysconnected to limit hydrostatic pump output pressure. The relief valve isunder the control of a control pressure from a relief valve modulatorvalve which is controlled by range TV pressure and G2 pressure. In thelowest drive range the relief valve modulator valve control pressure tothe relief valve controls maximum hydrostatic pump output pressure inaccordance with range TV pressure to prevent pump overload and controlpump power absorption to prevent engine stall. In all of the higherdrive ranges the maximum hydrostatic pump output pressure in addition tothe throttle pressure control is caused to decrease with increasing G2pressure to prevent overloading the hydrostatic pump during demandedhigh speed turns.

An object of the present invention is to provide a new and improvedpower train control system.

Another object is to provide a new and improved power train controlsystem providing both manual and automatic shifting.

Another object is to provide a power train control system having both amanual shift control and an auto matic shift control wherein theautomatic shift control remains available on discontinuance of power tothe manual control.

Another object is to provide in a power train control system a torqueconverter lockup control for interrupting lockup during range shiftingwhile holding lockup from zero to part engine throttle at low vehiclespeeds.

Another object is to provide in a power train control system a sequencecontrol to disengage a range drive on a directional change to permitdirectional drive engagement under no-load conditions.

Another object is to provide in a power train control system a manualshift control with automatic downshifting according to vehicle speed toa selected lower drive range.

Another object is to provide in a power train control system adirectional drive inhibitor inhibiting directional changes in the powertrains high drive ranges.

Another object is to provide in a power train range and steer controlsystem a shift inhibitor inhibiting automatic shifting during steeringoperation.

Another object is to provide in a power train control system anunmodulated main pressure source for directional drive engagement,control functions and control pressures and a modulated main pressuresource for drive range engagement and converter lockup.

Another object is to provide in a power train control system multiplethrottle pressures for different control functions including converterlockup range shifting and hydrostatic pressure relief.

Another object is to provide in a hydrostatic steer control of a powertrain control system a control pressure regulator modulating controlpressure for steer bias according to hydrostatic pump output pressure.

Another object is to provide in a hydrostatic steer control of a powertrain control system an overload stroke limiter limiting hydrostaticpump displacement in accordance with differential pressure across thehydrostatic pump.

Another object is to provide in a hydrostatic steer control of a powertrain control system a maximum hydrostatic pump output pressure reliefin accordance with engine throttle opening and vehicle speed.

Another object is to provide in a power train control systemelectrically actuated manual drive selection and automatic driveselection independent of electrical power.

Another object is to provide in a power train control system anelectrically actuated manual range selection and directional drive and afluid pressure actuated automatic range control automatically actuatedon discontinuance of electrical power for manual selection whiledirectional drive selection is maintained.

These and other objects of the present invention will be more apparentfrom the following description and drawings in which:

The power train and control system are shown schematically in FIGS. 2a,2b, 2c, 2d and 2e, when arranged as indicated by FIG. 1.

FIG. 3 is a view taken on the line 3-3 in FIG. 2d.

FIG. 4 is a perspective view with parts broken away of the operatorscontrol in the power train control system.

FIG. 5 shows the schedule of power train operation.

POWER TRAIN ARRANGEMENT The invention is illustrated in an arrangementcontrolling a track-laying vehicle power train which is of the typeshown in detail in the Livezey et al. US. Pat. No. 3,373,636 and iscapable of providing multiple speed or drive range and hydrostaticsteering operation in forward and reverse. The power train as shown inFIGS. 2a and 2d receives input from a prime mover 210 such as a pistonengine and generally comprises a hydrodynamic torque converter 211, aforward and reverse drive unit 212, a three-speed planetary gear rangeunit 213, a left steer unit 214, a right steer unit 216, a differentialunit 218, and a hydrostatic pump and motor steer unit 219 forcontrolling difierential unit 218, all housed in a housing 222. Thesecomponents are connected in the power train arrangement to provide fourspeed or drive ranges in forward and reverse and hydrostaticallycontrolled steering.

In the power train arrangement, the engine 210 is connected to drive thepower trains input shaft 224 which is connected by the converters rotaryhousing 226 to pump blading 228 (P). The pump blading 228 exits fluid toturbine blading 229 (T) which is connected by hub 231 to converteroutput shaft 232. Fluid is redirected to pump blading 228 by statorblading 234 (S) which is grounded to the power train housing forreaction by one-way brake 236. A converter lockup clutch 23% connectedbetween converter housing 226 and hub 231, when engaged, provides directmechanical drive between power train input shaft 224 and converteroutput shaft 232.

The converter output shaft 232 provides input to both the range unit 213and the differential unit 218 via the forward and reverse drive unit212, the range unit 213 providing one input to each of the steer units214 and 216 and the differential unit 218 providing another input toeach of the steer units. In the drive to forward and reverse drive unit212, the converter output shaft 232 is connected at its left end to agear 239 meshing with an idler gear 240. Idler gear 240 meshes with agear 241 which latter gear is connected to a shaft 242. Shaft 242 isconnected to clutch drum 244 of the forward and reverse drive unit 212.Drum 244 is connectible through either a forward or reverse drive toboth the range unit 213 and differential unit 218. For the forward driveunits 213 and 218, unit 212 has a forward drive clutch 246 which, whenengaged, connects drum 244 to a gear 247 geared to drive an annular gear248. In this gear drive, gear 247 meshes as illustrated schematically bythe dashed line with an idler gear 245 which latter gear meshes with thegear 248. Gear 248 is connected to a sleeve shaft 249 which is the inputshaft of range unit 213. Gear 247 also meshes with an annular gear 250which is connected to drum 251 of the differential unit 218, unit 218being described in more detail later. Thus, in the forward drive geartrain provided and with the forward drive clutch 246 engaged, shaft 242drives the range unit input shaft 249 in the same direction and thedifferential drum 251 in the opposite direction.

For the reverse drive to the units 213 and 218, a reverse drive clutch252 in unit 212 is engaged to connect drum 244 to an annular gear 254freely received on shaft 242. Gear 254 meshes with an idler gear 256which meshes with an annular gear 257. Gear 257 is connected by thedifferential drum 251 to the gear 250 at the other end of the drum. Thedrive is then from gear 250 via gears 247, 245 and 248 to the range unitinput shaft 249. Thus, with the reverse drive clutch 252 engaged, shaft242 drives the range unit input shaft 249 in the opposite direction andthe differential drum 251 in the same direction.

In the range unit 213, its input shaft 249 is connected to both theannular sun gear 258 of a low ratio planetary gear set 259 and theannular sun gear 261 of an intermediate ratio planetary gear set 262.The sun gear 258 meshes with pinions 264 joumaled on an output carrier266. Ring gear 268 of the low ratio gear set meshes with pinions 264, isconnected to carrier 269 of the intermediate ratio gear set, and may beheld by a low brake 271 to provide a low ratio drive to output carrier266. The sun gear 261 of the intermediate ratio gear set meshes withpinions 272 joumaled on carrier 269. Ring gear 274 of the intermediateratio gear set meshes with pinions 272 and may be held by anintermediate brake 276 to provide higher speed and intermediate ratiodrive to output carrier 266. A high clutch 278, when engaged, connectsthe range unit input shaft 249 to the intermediate carrier 269 andconnected low ring gear 268 to lock the low ratio gear set 259 toprovide direct drive between the range unitts input and output.

The range unit output carrier 266 is connected by a hub 279 to rangeunit output shaft 280 which extends freely through sleeve shaft 249,shaft 280 serving as both the range units output shaft and the steerunits input shaft. Shaft 280 is connected at its left end to ring gear281 of a planetary gear set 282 in left steer unit 214 and at its rightend to ring gear 284 of a planetary gear set 286 in right steer unit216, gear sets 282 and 286 having equal speed ratios.

On the left side, the ring gear 281 of gear set 282 meshes with pinions287 joumaled on an output carrier 288. An annular sun gear 290 freelyreceived on shaft 280 meshes with pinions 287 and is connected to becontrolled by the differential unit 218 as described in more detaillater. A drum 291 connects carrier 288 to the power train 's left outputshaft 292 which shaft is for powering the vehicles left track. Amechanical brake 299 and a hydrodynamic brake 300 are both connected tobrake the power train s left output shaft 292.

On the right side, the ring gear 284 of gear set 286 meshes with pinions301 joumaled on an output carrier 302. A drum 303 connects carrier 302to the power trains right output shaft 304 for powering the vehicle 'sright track. An annular sun gear 306 freely received on shaft 380 mesheswith pinions 301 and is connected to be controlled by the differentialunit 218. A mechanical brake 316 and a hydrodynamic brake 317 are bothconnected to brake the power trains right output shaft 304.

A low low brake 318, when engaged, is connected by the hub 279 to holdshaft 280 and the connected ring gears 281 and 284 of the steer units.This enables the sun gears 290 and 306 of the steer units to producedrive in the steer units without output from the range unit and at thelowest available ratio as described in more detail later.

Describing the hydrostatically controlled differential unit 218, the sungears 290 and 306 of the steer units are continuously connected by equalspeed ratio and direction reversing gear trains to output carriers 322and 324 of equal speed ratio planetary gear sets 326 and 328,respectively, provided in unit 218. The left gear train comprises anannular gear 325 which is connected to sun gear 290 of the left steerunit and meshes with an annular gear 323. Gear 323 is connected by asleeve shaft 327 to the left output carrier 322 of unit 218. The rightgear train similarly comprises an annular gear 328 which is connected tosun gear 306 of the right steer unit and meshes with an annular gear329. Gear 329 is connected by a sleeve shaft 330 to the right outputcarrier 324 of unit 218. The ring gears 331 and 332 of gear sets 326 and328 are both connected to the drum 251 driven by the forward and reversedrive unit 212. Pinions 334 joumaled on the left output carrier 322 meshwith the ring gear 331 and a sun gear 336. Similarly, pinions 338joumaled on the right output carrier 324 mesh with the ring gear 332 andan annular sun gear 339. The sun gears 336 and 339 mesh with meshingdifferential pinions 341 and 342, respectively. The differential pinions341 and 342 are joumaled on spindles attached to a differential carrier344 which is continuously grounded to the power train housing by a shaft346 which extends through annular sun gear 339.

Hydrostatic control of difierential unit 218 is provided by thehydrostatic unit 219 shown in FIG. 2d

operating on sun gear 336 of differential unit 218 which sun gear isconnected by a shaft 349 to a gear 351, shaft 349 extending throughsleeve shaft 327 to make the connection. Gear 351 meshes with a gear 352which latter gear is connected by a motor output sleeve shaft 354 to thehydrostatic motor 356. The hydrostatic pump 358 is input driven througha gear train which has an annular gear 359 connected to the converterhousing 226 and meshing with an idler gear 361. Gear 361 meshes with anannular gear 365 which is connected by a pump input sleeve shaft 367 tothe hydrostatic pump 358, the input shaft 242 of the forward and reversedrive unit 212 extending freely through both shafts 367 and 354.Preferably, the hydrostatic pump 358 and hydrostatic motor 356 areaxially aligned as one unit and located between the gears 36S and 352with their central axis coinciding with that of the shaft 242 which thenextends freely through the hydrostatic pump and motor steer unit. Thepump 358 has a variable displacement and the motor 356 has a fixeddisplacement and the hydrostatic unit is conditionable to hold motoroutput shaft 354 and to drive the motor output shaft in either directionat infinitely variable speed.

The drive producing clutches and brakes are conventional friction driveestablishing devices of the friction plate type each having a suitablefluid motor which is operated by fluid pressure to effect engagement ofthe device. Each of these devices also has suitable retraction springmeans, not shown, that operate on exhaust of the fluid pressure toeffect disengagement of the device. The output mechanical brakes 299 and316 have conventional structure and are operated simul taneously byconventional linkage which includes a rotary or otherwise movable membersuch as shaft 370 shown in FIG. 20 which shaft turns during engagementand disengagement of these brakes.

OPERATION OF POWER TRAIN ARRANGEMENT The power train may be operated toprovide four speed or drive ranges in forward and reverse andhydrostatically controlled steering. The first (l) or low low driverange which is considered the lowest drive range and provides thegreatest torque multiplication is established by engaging the forwarddn've clutch 246 in the case of forward drive and the low low brake 318and conditioning the hydrostatic steer unit 219 to hold the motor outputshaft 354 and thus the controlled sun gear 336 in differential unit 218,all other drive establishing devices being disengaged. Since the carrier344 in the differential unit is grounded and the sun gear 336 is held bythe hydrostatic steer unit, rotation of the other sun gear 339 is alsoprevented. With ring gears 331 and 332 of the differential unit beingdriven at the same speed and in the same direction by converter 211through the forward drive clutch 246, the differential output carriers322 and 324 are driven in the same direction at the same speed by lockeddrives. Thus, the sun gears 290 and 306 of steer units 214 and 216 aredriven in the same direction which is forward and at the same speedwhile both of the ring gears 281 and 284 of the steer units are held bythe low low brake 318. Therefore, the gear sets 282 and 286 in the steerunits act as reduction gear sets with the locked input drives thusprovided to drive the power train output shafts 292 and 304 in theforward direction at the same speed. When the speed of the converterturbine 229 reaches a desired value the lockup clutch 238 is engaged toprovide mechanical drive instead of the hydraulic drive the rough theconverter.

In the differential unit 218, rotation of sun gear 336 in eitherdirection with the infinitely variable speed drive made available by thehydrostatic steer unit 219 results in opposite rotation of sun gear 339at the same speed. Thus, the outputs carriers 322 and 324 and their geartrain connected sun gears 290 and 306 of the steer units are driven atequal differential speeds measured from their same base speed with sungear 336 held since the speed of these carriers is determined by thecombination of the equal speed ratio drive to the connected ring gears331 and 332 and the equal speed opposite directional drive to the sungears 336 and 339.

Thus, for steering in the first forward drive range the hydrostaticsteer unit 219 is conditioned so that instead of continuing to hold thedifferential units sun gear 336, it then drives the controlled sun gear336 in either direction depending on the direction of vehicle turndesired. Then, with sun gear 336 rotating in one direction, the otherdifferential sun gear 339 is caused to rotate in the opposite directionat the same speed. The combined differential action in the gear sets 326and 328 that results causes, as for example when sun gear 336 is drivenin the same direction as the ring gears 331 and 332, the carrier 322 tospeed up by the same amount that the carrier 324 is being slowed down.In this manner the sun gears 290 and 302 in the steer units aredifferentially driven in the same direction or in opposite directionswith locked differential drives, recognizing that the left sun gear 290,for example, will be speeded up by the same amount that the speed of theright sun gear 306 is diminished to thereby establish the differentialsteering. The steering radius is thus put under positive control andmade infinitely variable by units 218 and 219 from straight ahead drivein the first drive range down to the minimum radius possible withgearing provided.

The three higher drive ranges (2, 3, 4) in the forward direction areestablished by driving the connected ring gears 281 and 284 in the steerunits forward at different speeds with the forward clutch 246 remainingengaged, the sun gear 336 of the differential gear unit 218 held by thehydrostatic steer unit 219 and selective conditioning of the range unit213 to provide its low ratio drive (low brake 271 engaged), intermediateratio drive (intermediate brake 276 engaged), and high ratio drive (highclutch 278 engaged) in that order. in these three higher drive ranges,the steer units then act as power combining and speed difierentialdevices receiving power from both the range unit 213 and thedifferential unit 218. Hydrostatically controlled differential steeringis available in these higher ranges by control of the hydrostatic steerunit 219 to provide locked difierential drive as described in the firstdrive range, recognizing that the speed added to one of the steer unitsun gears will be equal to the speed subtracted from the opposite steerunit sun gear while the connected ring gears of the steer units continueto rotate forwardly with their drive from range unit 213. Thus, theoutput speed in one steer unit is increased by the amount the outputspeed of the other steer gear unit is diminished to provide thedifferential steering. Again, the steer radius is under positive controland infinitely variable in the second, third and fourth forward driveranges from straight ahead down to the minimum radius possible with thegearing provided.

Since the forward and reverse drive unit 212 provides the input to boththe range unit 213 and differential unit 218, the same drive ranges andhydrostatically controlled difierential steering provided in forward asdescribed above, are also available in reverse by simply disengaging theforward drive clutch 246, engaging the reverse drive clutch 252 andoperating range unit 213 and hydrostatic steer unit 219 as before.

For neutral, either the forward or reverse drive clutch is preferablyengaged, all other drive establishing devices are disengaged, the sungear 336 of the differential unit 218 is held by the hydrostatic steerunit 219 and there is no output drive to the power train output shafts292 and 304. Steering in neutral is provided by controlling thehydrostatic steer unit 219 to drive the sun gear 336 in the differentialunit 218 in either direction dependent on the direction of vehicle turndesired. This causes the opposite sun gear 339 of the differential gearunit to rotate in the opposite direction at the same speed and since thedrum 251 is acted on by opposed gear forces, the connected ring gears331 and 332, though free, provide reaction in their gear sets. Thus, theoutput carriers 322 and 324 of the differential unit are caused torotate at equal speeds in opposite directions. Because the sun gears 290and 306 of the steer units are being driven in opposite directions andat the same speed by the free differential drives provided by unit 218,the connected ring gears 281 and 284 of the steer units, though free,provide reaction resulting in the power train output shafts 292 and 304being driven at equal speeds in opposite directions to produce pivotsteering.

CONTROL SYSTEM The control system for this power train arrangement andaccording to the present invention provides for both automatic andmanual selection of the four drive ranges in both forward and reverseand steering control in all drive ranges and neutral. Other functions ofthe control system include lubrication, cooling, charging of the torqueconverter, and charging of the hydrodynamic brakes.

FLUID SUPPLY The fluid such as oil used in all of the control functionsis supplied by four gear-type positive displacement pumps shown in P16.20 which draw from a reservoir 481) to which the fluid exhaust from allparts of the system is returned. Fluid which tends to accumulate incertain locations in the power train housing 222 is scavenged by one ormore input driven scavenge pumps, not shown, which remove this excessfluid and return it to the reservoir.

The pump 402, which is called the hydrostatic supercharge-converterpump, is drivingly connected to the power train input shaft 224 so thatit is continuously driven to supply fluid when the engine is operating.This pump supplies both the hydrostatic steer portion and the torqueconverter portion of the system.

The pump 404, which is called the coolant pump, is drivingly connectedto the converter turbine 229 so that it is driven to supply fluid whenthe converter turbine is being driven. The fluid supplied by this pumpis delivered to charge the hydrodynamic output brakes 300 and 317 withthis same fluid then being used to flood the friction plates of themechanical output brakes 299 and 316 to cool them during theirengagement.

The pump 406, which is called the main pressure input pump, is drivinglyconnected to the power train input shaft 224 so that it is continuouslydriven to supply fluid when the engine is operating. The fluid suppliedby this pump furnishes the main fluid supply to the shift controlportion of the control system which controls the shifting of the powertrain and also delivers fluid to lubricate various parts of the powertrain.

The pump 408, which is called the main pressure output pump, isdrivingly connected to one of the power train output shafts, outputshaft 292 for example, so that it is driven to supply fluid only whenthe vehicle is moving forwardly. The fluid supplied by this pumpsupplements the fluid supply from the main pressure input pump 406during forward drive operation and is the only source of main pressuresupply when the main pressure input pump is not operating.

HYDROSTATIC SUPERCHARGE PRESSURE REGULATOR VALVE The hydrostaticsupercharge-converter pump 402 draws fluid from the reservoir 400 viaintake line 410 and delivers this fluid to a hydrostatic supercharge-converter supply line 412. Line 412 as shown in FIG. 2a is connected to achamber 414 in one end of the valve body of a hydrostatic superchargepressure regulator valve 416 which in addition to providing a regulatedlow pressure source for the hydrostatic portion of the control systemadmits fluid to the torque converter 211. Regulator valve 416 has aregulator valve element 418 with a land a located in bore 420 of asleeve 422 secured in the valve body. A valve stem 424 bottomed on aretaining ring 426 has a land a located in a blind bore 428 in the lowerend of regulator valve element 418 to provide a damping chamber 430.Chamber 430 is continuously connected by an orifice 432 and an elongatedannular channel 433 in regulator valve element 418 to the controlsystems main line which has fluid at main pressure as described in moredetail later. The force of a spring 434 arranged between the re gulatorvalve element 418 and the base of the valve stem 424 plus the mainpressure in damping chamber 430 urge the regulator valve element 418upward toward closed position shown, the closed position determined byshoulder 436 of valve element 418 abutting collar 438 of sleeve 422. Theregulator valve element 418 in its closed position closes a converter-inline 440 from the hydrostatic supercharge-converter supply line 412.These forces are opposed by the pressure from line 412 acting on thefull upper end area of land a of regulator valve element 418 which urgesthe regulator valve element downward toward an open position connectingline 412 to the converter-in line 440 through porting 441 in sleeve 422.The spring bias of the regulating spring 434 plus the pressure bias inchamber 430 provide for regulation of pressure (hydrostatic superchargepressure) in line 412 to the desired value with the overage delivered tothe converter-in line 440. The damping chamber 430 with its restrictedconnection by orifice 432 to the control system's main line prevents theshoulder 436 from battering the collar 438 during the pressureregulation.

CGNVERTER PRESSURE REGULATOR VALVE The pressure of the fluid admitted bythe hydrostatic supercharge pressure regulator valve 416 to theconverter-in line 440 is reduced to either one of the two lowerregulated pressures by a converter pressure regulator valve 442 shown inFIG. 2a. The high regulated pressure provided by the converter pressureregulator valve 442 is for normal converter operation and the lowregulated pressure is for lockup operation with the lockup clutch 238engaged. The converter-in line 440 is connected to a chamber 444 in theupper end of the valve body of regulator valve 442 which has a regulatorvalve element 446 guided by a rod 448 extending through central bore 450in the valve element. The rod 448 is secured at its lower end to a plug452 located in bore 454 of the valve body, plug 452 in cooperation withbore 454 providing a chamber 456. A spring 458 arranged between theregulator valve element 446 and plug 452 urges the regulator valveelement upward toward the closed position shown. The regulator valveelement 446 in its closed position closes the chamber 444 and connectedconverter-in line 440 from an exhaust 460. The closing force is opposedby pressure from the converter-in line 440 acting in chamber 444 on theregulator valve element 446, this pressure urging the regulator valveelement downward toward an open position connecting the chamber toexhaust 460. The low regulated pressure is provided when the chamber 456is exhausted and the plug 452 is bottomed so that the normal bias ofregulating spring 458 determines the opening and closing of the valve.

The high regulated pressure by converter pressure regulator valve 442 isprovided when a pressure signal is delivered to the chamber 456 from thelockup shift control portion of the control system as described in moredetail later. The pressure delivered to chamber 456 raises the plug 452upward to the position shown in which it abuts with a stop ring 461thereby increasing the bias applied by spring 458 to the regulator valveelement 446 to effect the high pressure regulation. An elongatedexternal annular channel 462 in the plug 452 is supplied with fluid fromthe control system's main line described later so that the plug floatson a constant film of fluid allowing it to move readily between its lowand high pressure positions.

The fluid at pressure regulated by the converter pressure regulatorvalve 442 is delivered by the converterin line 440 to the torqueconverter 211. The fluid leaves the converter by a converter-out line464 which passes it through a cooler 466 located externally of the powertrain housing prior to returning it to the reservoir 400, therestriction to flow through the converteroutline 464 and cooler 466maintaining pressure at the converter outlet.

The capacity of the hydrostatic supercharge-converter pump 402 issufficient to meet the requirements of both the hydrostatic portion ofthe control system and the torque converter during all their operatingconditions, the high charging pressure for converter operationmaintaining the converter filled with fluid while effecting sufficientflow to carry away heat for dissipation in the cooler. During lockupoperation, the converter requires a smaller volume of fluid which iseflected by the low regulated pressure provided by the converterpressure regulator valve 442.

HYDRODYNAMIC BRAKES The coolant pump 404 is operable to draw fluid fromthe reservoir 400 via an intake line 468 through a check valve 470 anddeliver the fluid to a coolant line 472 as shown in FIG. 2c. Coolantline 472 is connected to cavities 474 and 476 of the hydrodynamic brakes300 and 317, respectively, as shown in FIG. 2a. With rotors 478 and 480of the hydrodynamic brakes 300 and 317, respectively, rotating throughtheir fluid-filled cavity, there is provided hydrodynamic braking of thepower train output shafts. When pump 404 isoperating the fluidcontinuously passes through the cavities 474 and 476 and is directed bymechanical brake coolant lines 482 and 484 to cool the friction platesof the mechanical output brakes 299 and 316, respectively.

AIR VALVE Control over delivery of fluid by the coolant pump 404 to thehydrodynamic and mechanical output brakes is provided by an air valve486 shown in FIG. 2c. Air valve 486 has a valve element 488 which in theopen position shown opens chamber 490 in the valve body via a port 491to an air line 492, chamber 490 being open to atmosphere. Air line 492is connected to the intake side of the coolant pump 404 upstream ofcheck valve 470. Thus, when the coolant pump is being driven with theair valve 486 open, the check valve 470 closes and the coolant pump isair bled and delivers only air to the cavities of the hydrodynamic andmechanical output brakes thereby belljarring these cavities to force anyfluid therein back to the reservoir. When the air valve element 488 ismoved to a closed position closing port 491 and thus closing the airline 492 to the atmospheric chamber 490, air is prevented from enteringthe intake side of the coolant pump which then operates to draw fluidthrough the check valve 470 for delivery to the brakes.

The opening and closing of the air valve 486 is under the control of themechanical linkage which operates the mechanical output brakes 299 and316. The valve element 488 is secured to the upper end of a right-anglearm 494 which is pivoted at its bend on a pivot pin 496 secured in thevalve body. The lower end of arm 494 has an aperture through which acontrol rod 498 extends, the rod being mounted for reciprocal movementin stepped bore 499 in the valve body. When the mechanical output brakesare disengaged, shaft 370 of their linkage is in the angular positionshown in FIG. 20. An arm 500 splined to shaft 370 engages the projectingleft end of control rod 498 so that while the mechanical output brakesare disengaged, a spring 502 mounted in a bore 503 in the valve body andbetween a screw plug 504 and the lower end of arm 494 holds the latteragainst a collar 506 on the control rod 498. This positions and holdsthe valve element 498 in its open position so that the coolant pump 404is air bled when the mechanical output brakes are disengaged. When themechanical output brakes are engaged by the operator,

shaft 370 is pivoted counterclockwise as shown by the directional arrow.This swings arm 500 counterclockwise and the spring 502 forces thecontrol rod 498 to follow arm 500 while forcing the lower end of arm 494to follow the collar 506 and swing valve element 488 to its closedposition, the collar 506 abutting shoulder 501 in bore 499 to limit theleftward movement of the control rod. With the air valve 486 closed thecoolant pump 404 is no longer air bled and then delivers fluid to thebrakes as previously described. The motion of the mechanical linkageoperating the mechanical brakes is such that the air valve 486 closesprior to initial engagement of the mechanical output brakes so that thehydrodynamic brakes are put in operation first to retard the vehiclesMAIN PRESSURE REGULATOR VALVE The main pressure input pump 406 drawsfluid from the reservoir 400 via intake line 508 and delivers this fluidto a main line 510. Themain pressure .output pump 408 draws fluid fromthe reservoir via an intake line 512 and delivers this fluid through acheck valve 514 to main line 510. The fluid delivered to main line 510from these pumps is passed through a filter 516 prior to flowing to alldownstream portions of the control system.

The main pressure supply for the shift control portion of the controlsystem is regulated in main line 510 by a main pressure regulator valve518 shown in FIG. 2c, the valve delivering the excess fluid to lubricateparts of the power train. The main pressure regulator valve 518 has aregulator valve element 520 having lands a and b of equal diameterlocated in bore 522 of the valve body. Regulator valve element 520 isnormally biased to the right to the position shown by two springs 524and 526. The spring 524 is located between left end wall 527 of thevalve body and a shoulder 530 on the regulator valve element 520. Thespring 526 is located in a blind bore 532 in the left end of theregulator valve element 520 and between the regulator valve element anda plug 536 which is bottomed at its left end on the valve body wall 527,the regulator valve element being movable with respect to plug 536. Themain line 510 is always connected to the bore 522 in the space betweenlands a and b. This space is always connected to a passage 538 inregulator valve element 520 having a spring loaded ball check valve 540therein permitting fluid flow from the main line 510 to the bore 522between land b and right end wall 542 of the valve body. The fluidadmitted to the right end of the valve bore 522 acts on the exposed andarea of land b so that I the valve regulates the pressure in main line510 with the normal action of the regulating springs 524 and 526. Thecheck valve 540 in cooperation with an orifice 544 through land b darnpsthe action of the regulator valve. The fluid overage resulting from theregulating action upon leftward regulator valve element movement tomaintain the main line pressure is delivered to a lubrication line 546.

The action of regulating springs 524 and 526 with no assist establishesa low main pressure in main line 510. This low main pressure is usedwhen the control system is controlling third and fourth drive rangeoperations in either forward or reverse and neutral. When the powertrain is operating in the first and second drive ranges in eitherforward or reverse, the regulating springs are assisted by fluidpressure to boost main line pressure to a higher regulated value. Theregulated high main pressure is provided by directing a signal pressureindicating first and second drive range operation to a port 548 in thevalve body which is continuously connected by a channel 550 in land a ofthe regulator valve element 520 and a passage 552 to chamber 554 in theleft end of the regulator valve element, such chamber being provided bythe bore 532 and plug 536. The fluid pressure thus delivered to thechamber 554 acts leftward on the bottomed plug 536 and rightward on theregulator valve element 520 thereby assisting the regulating springs andboosting the regulated pressure in main line 510 to the higher value.

The main pressure, when it is at either its low or high value, isdecreased during converter lockup operation. This is perrnissable sincelower torque at higher rotating speeds is being transmitted through thepower train. To this end, the regulator valve element 520 has a reduceddiameter portion 556 which extends through an aperture in the end wall542 of the valve body into a chamber 558. When fluid pressure indicatinglockup operation is delivered to the chamber 558 as described in moredetail later, such pressure acts leftward on the regulator valve element520 to decrease main line pressure.

The main line 510 is connected to the damping chamber 430 of thehydrostatic supercharge pressure regulator valve 416 and channel 462 ofthe converter pressure regulator valve 442. Thus, fluid at the mainpressure is supplied to these valves for their operations as previouslydescribed.

FORWARD AND REVERSE MAIN PRESSURE REGULATOR VALVE Main line 510 is alsoconnected to a forward and reverse main pressure regulator valve 560which is shown in FIG. 20. Valve 560 has a regulator valve element 561with lands a and b of equal diameter located in bore 562 of the valvebody. The valve element 561 is normally biased to the open positionshown by spring 564. A forward and reverse main line 566 is alwaysconnected to a passage 567 in the valve element having a spring loadedball check valve 568 therein permitting fluid flow from the forward andreverse main line 566 to the right end of the valve bore 562. The fluidin the right end of the valve bore acts leftward on the full end area ofland b to close the connection to main line 510 so that the valveregulates the pressure in the forward and reverse main line 566 eventhough main pressure is subject to modulation which gives severalpressure levels as previously described. The check valve 568 incooperation with a small clearance between land b and the bore 562darnps the action of the regulator valve.

GOVERNORS The control system has two fluid velocity governors providingseparate speed governed pressures. These pressures are used to controldifferent operations in the control system.

One governor 569 called the G1 governor is shown in FIG. 2a and has anannular trough 570 connected to the power train shaft 242 which isdriven by the converter turbine 229. The annular trough 570 ismaintained suitably filled with fluid from the lubrication line 546 viaorifice 571 shown in FIG. 20. This fluid impinges on the open end of apitot tube 572 to provide in a 61 line 573 a governor pressure (G1pressure) which is proportional to converter turbine speed.

The other governor 574 called the G2 governor is also shown in FIG. 2aand has its annular trough 575 connected to the range unit output shaft280. The trough 575 is maintained suitably filled with fluid from thelubrication line 546 via orifice 571 like the GI governor 56?. Thisfluid impinges on either open end of a double ended pitol tube 576having a two way check valve between the open ends to provide in a G2line 577 a governor pressure (G2 pressure) which is proportional tovehicle speed in second, third and fourth drive range operations inforward and reverse, the range unit output shaft 280 being stationary inthe first drive range in forward and reverse.

PRIMARY THROTTLE PRESSURE REGULATOR VALVE AND SECONDARY THROTTLEPRESSURE REGULATOR VALVE Three pressures indicating engine torque demandand used primarily for control of various automatic operations in thecontrol system are provided. These are T pressure, TV pressure and rangeTV pressure. The T and TV pressures are derived from forward and reversemain pressure in the line 566 by a primary throttle pressure regulatorvalve 580 (primary TV valve) and the range TV pressure is derived fromforward and reverse main pressure in line 566 by a secondary throttlepressure regulator valve 582 (secondary TV valve), both of these valvesbeing shown in FIG. 20.

The primary TV valve 580 has a regulator valve element 584 having landsa and b of equal diameter located in a small diameter portion of a bore586 in the valve body. The valve also has a control valve element 587having lands a and b of equal diameter and larger in diameter than thelands of valve element 584 located in a large diameter portion of bore586. A zero or closed throttle to full throttle regulating spring 589and a detent spring 590 of shorter length are located between the twovalve elements 584 and 587.

The positioning of the control valve element 587 is controlled by athrottle cam 591 which contacts the projecting right end of the controlvalve element 587 and is pivoted by pivot pin 592 on the valve body, thethrottle cam 591 being connected by suitable linkage to the enginethrottle control, not shown, which controls the throttling of the engine210. When the engine throttle is closed or at zero throttle position,the cam 591 is against a stop 5% and the two valve elements 584 and 587are positioned as shown with the outer spring 589 positioning thecontrol valve element 587 against the cam 591. At the zero position ofthe control valve element 587 which corresponds to closed enginethrottle, there is no spring loading on the regulator valve element 584and its land a blocks the forward and reverse main line 566 so that a TVline 594 receives no pressure, TV line 594 being continuously connectedto the space between lands a and b of the regulator valve element. Asthe engine throttle is opened, the cam 591 is pivoted clockwise movingthe control valve element 587 leftward. This leftward movement causesthe spring 589 to load the regulator valve element 584 and opens theforward and reverse main line 566 so that fluid is delivered betweenlands a and b of the regulator valve element to the TV line 594. The TVline 594 is always connected to a passage 595 in the regulator valveelement 584 having a spring loaded ball check valve 596 thereinpermitting fluid flow from the TV line 594 to chamber 597 at the leftend of the valve body. The fluid pressure in chamber 597 acts rightwardon the full end area of land a so that the valve regulates to provide TVpressure in the TV line 594 according to the acting spring bias ofregulating spring 589 with overage being delivered to an exhaust 598.The TV line 594 is also connected to the chamber 597 through an orifice600 so that the ball check valve 596 in cooperation with the orifice 600darnps the regulating action of the valve. An exhaust 601 exhausts anyleakage that otherwise might collect in bore 586 between valve elements584 and 587.

Since movement of the valve element 587 is proportional to the enginethrottle opening which is indicative of engine torque demand, the springload thus provided on the regulator valve element 584 is alsoproportional to engine throttle opening and indicative of engine torquedemand. Thus, the TV pressure produce in TV line 594 is proportional toengine throttle opening and increases with increasing throttle openingand torque demand.

The control valve element 587 at a point corresponding to full enginethrottle opening and near the elements limit of leftward travel, forexample, begins pressing the detent spring 590. Thus, leftward movementof control valve element 587 past 80 percent travel causes the detentspring 590 to load the regulator valve element 584 in addition to thespring bias of spring 589 while the linkage to the engine throttlepassesthrough a detent. Thus, through detent past full engine throttle,TV pressure increases rapidly at an increased rate to its maximum.

The TV line 594 is always connected at bore 586 around the control valveelement 587 and through the valve body as shown. The control valveelement 587 at a point about midway through its maximum travel, 40percent for example, connects the TV line 594 between the elements landsa and b to a T line 604 and throughout the remainder of leftwardmovement of the control valve element. The TV pressure delivered to theT line 604 provides the T pressure which is thus the upper part of therange of TV pressure in TV line 594.

The secondary TV valve 582 has a regulator valve element 605 with equaldiameter lands a and b located in a bore 606 of the valve body. Aregulator spring 608 biases the regulator valve element 605 leftward toconnect the forward and reverse main line 566 via the space betweenlands a and b to a range TV line 610 which is always connected to thisspace. This space is always connected to a passage 612 in the regulatorvalve element having a spring loaded ball check valve 614 thereinpermitting flow from the range TV line 610 to a chamber 616 at the leftend of the valve body. The fluid pressure in chamber 616 acts on thefull end area of land a to urge the regulator valve element 605rightward against the spring bias. With rightward movement of regulatorvalve element 605, land a closes the connection to the forward andreverse main line 566 and opens the range TV line 610 between lands aand b to the TV line 594. The range TV line 610 is connected through anorifice 618 to chamber 616 so that the orifice and check valve 614cooperatively provide for damping regulator valve element movementduring pressure regulation. An orifice 619 exhausts any leakage thatmight otherwise collect in the right end of bore 6116.

The secondary TV valve 582 regulates to provide minimum range TVpressure in range TV line 610 according to the bias of regulator spring608 as long as overage can exhaust the the TV line 594, i.e., range TVpressure is greater than TV pressure. When TV pressure is equal to orgreater than the minimum range TV pressure determined by the regulatorspring 608, overage exhaust is prevented by TV pressure. TV pressure isthen transmitted from the lockup TV line 594 to the range TV line 610 bywhat was before the regulator exhaust connection of the secondary TVvalve 582. The TV pressure in the range TV line 610 is transmitted tochamber 616 where it acts to hold the regulator valve element 605 inwhat would normally be its exhaust position so that the TV pressureconnection is maintained when TV pressure is equal to or greater thanthe minimum range TV pressure.

Thus, the minimum range TV pressure in line 610 is provided byregulating action of the secondary TV valve 582. Higher range TVpressure in line 610 is provided by TV pressure through the valve uponcessation of its regulating action when TV pressure is equal to orgreater than the minimum range TV pressure.

FLOW VALVE The main line 510 is connected to a range main line 626 by aflow valve 628 shown in FIG. 2e. Flow valve 628 has a valve element 630having lands a and b of equal diameter located in portion 632 of astepped bore 633 in the valve body and a land of larger diameter locatedin bore portion 634. Main line 510 is connected to the left end of bore633 to act rightward on the full end area of land a and is connected tothe range main line 626 via an orifice 636 in the valve body. The rangemain line 626 is connected via an orifice 638 to the right end of bore633 where it acts leftward on the full end area of the larger land 0.

When there is no flow from main line 510 to range main line 626 throughorifice 636, the pressures on the opposite ends of the flow valveelement 630 are equal and the pressure on the larger land c holds thevalve in the no-flow position shown. In the no-flow position the valveelement 630 connects the G1 line 573 between lands a and b to aGl-lockup line 639 and land b blocks a Gl-exhaust line 640 from thespace between lands a and b.

When there is flow, which occurs during a range shift, the pressure dropwhich results at the orifice 636 reduces pressure in the range main line626 and thus the pressure acting on the larger land c. This pressurereduction is sufficient to cause the valve element 630 to move rightwardto a lockup cutoff or flow position. Rapid rightward movement of theflow valve element 630 is permitted by a ball check valve 641 whichunseats to permit flow from the right end of bore 633 to the range mainline 626. In the lockup cutoff position, land a of valve element 636blocks the G1 line 573 and 18 the G1 lockup line 639 is connectedbetween lands a and b to the G1 exhaust line 640.

After the range shift is made, pressure increases in the range main line626 until the pressures at each side of the flow valve orifice 636 areagain equal. When this occurs, the check valve 641 closes and fluidflows back into the right end of bore 633 through the orifice 638 whichbypasses the check valve 641. The return flow through orifice 638 isslower than the flow through the check valve 641 and thus the leftwardmovement of the flow valve element 630 that results is slower than therightward movement. An exhaust 642 connected at the step in bore 630between lands b and c prevents hydraulic locking of valve element 630.

FLOW VALVE MODULATOR VALVE A flow valve modulator valve 646 shown inFIG. 2e provides for normal operation of the flow valve 628 to controlconnection of the Gl-lockup line 639 between the G1 line 573 and exhaustabove a predetermined part engine throttle opening on a range shift andbypasses the normal action of the flow valve 628 below this enginethrottle opening so that the G1 line 573 and Gl-lockup line 639 remainconnected on a range shift. The flow valve modulator valve 646 has avalve element 648 having lands a and b located in a bore 650 of thevalve body. The valve element 648 is biased upward by a spring 652 to abypass position connecting the G1 line 573 between lands a and b to theGl-exhaust line 640. Thus, when the flow valve 628 is in its lockupcutoff position and the flow valve modulator valve 646 is in its bypassposition, the G1 line 573 remains connected to the Gl-lockup line 639.

The TV line 594 is connected to the upper end of bore 650 so that TVpressure acts downward on the full end area of land a of the valveelement 648 against the spring bias. The TV pressure above apredetermined part engine throttle opening prevails over the spring biasand moves the valve element 648 to the exhaust position shown connectingthe G1 exhaust line 640 between lands a and b to an exhaust 653 whileland a blocks the G1 line 573. Thus, when the flow valve 638 is in itslockup cutoff position and the flow valve modulator valve 646 is in itsexhaust position the G l-lockup line 639 is disconnected from the G1line 573 and connected to exhaust 653.

LOCKUP VALVE A lockup valve 654 shown in FIG. 2c controls the deliveryof main pressure in main line 510 to a lockup clutch motor 656 shown inFIG. 2a which operates the converter lockup clutch 238. The lockup valve654 has a valve element 658 having lands a, b and c of equal diameterand a G1 plug 660 of larger diameter located in a stepped bore 662 inthe valve body. A spring 666 located in the left end of the bore urgesthe shift valve element 658 and the G1 plug 660 to the position shownwhich is the release position. In this position a lockup clutch line 668connected to both the lockup clutch motor 656 and the chamber 558 of themain pressure regulator valve 518 is exhausted between lands b and c toexhaust 670. Thus, the lockup clutch 238 is released and main pressureis regulated at its low value by the main pressure regulator valve 518.In addition, the lockup valve 654 when in the release position connectsl9 main line 510 between the lands a and b to a converter signal line672 which is connected to chamber 456 of the converter pressureregulator valve 442. Thus, converter-in pressure is regulated at itshigh value by the converter pressure regulator valve 442 for normalconverter operation with the lockup clutch released.

The lockup valve element 658 is biased to the left to an apply or lockupposition by G1 pressure under the control of the flow valve 628 and theflow valve modulator valve 646. This is provided by connection of theGl-lockup line 639 to the bore 662 between the G1 governor plug 660 anda closure plug 673 which closes the right end of the bore. Thus, G1pressure acting leftward on the full end area of the G1 governor plug660 provides this bias only when the flow valve 628 is in its no-flowposition with no range shift occurring or in its lockup cutoflpositionon the occurrence of a range shift but with modulator valve 646 in itsbypass position below the predetermined part engine throttle opening.When the flow valve 628 is in its lockup cutoff position with theoccurrence of a range shift and the flow valve modulator valve 646 is inits exhaust position below part engine throttle opening, the G1 presureis exhausted from the lockup valve 654. An exhaust 671 preventshydraulic lock between plug 660 and valve element 658.

A controlled fluid pressure bias at the lockup valve 654 which assiststhe fixed bias of spring 666 in opposing the G1 pressure bias isnormally provided by the TV pressure and is assisted by the T pressurewhen the latter becomes available. When the lockup valve element 658 isin the release position shown, the TV line 594 is connected past land ato chamber 674 in the left end of the bore. The T line 604 is connectedby a ball check valve 676 to the chamber 674 and the chamber is alwaysconnected through an orifice 678 to an exhaust 680. The orifice 678maintains the pressure in chamber 674 when it is receiving fluid andrelieves the chamber of pressure when there is no supply. The checkvalve 676 prevents TV pressure from reaching the T line 604 during thetime when no T pressure exists which occurs during zero and part enginethrottle opening (-40percent travel of the primary TV valve element587).

When converter turbine speed is sufiicient to allow lockup clutchoperation, G1 pressure which is proportional to converter turbine speedis sufficient to move the lockup valve element 658 leftward to its applyposition, The TV pressure which is always available beyond closed enginethrottle admitted to chamber 674 past land a inhibits the initialleftward movement of the lockup valve. As the lockup valve element 658moves leftward, land a blocks delivery of TV pressure and the chamber674 is exhausted through orifice 678 to provide further leftwardmovement by snap action against the spring bias after TV pressure hasbeen overcome. Thus, when the lockup valve element 658 is in its applyposition and T pressure is not available, lockup clutch release isdelayed by requiring a lower G1 pressure (lower converter turbine speed)to enable the spring bias to move the lockup valve element to itsrelease position.

The T pressure which is provided by TV pressure only from 40 through 100percent travel of the primary TV valve element 587 is delivered throughthe check valve 676 to chamber 674 of the lockup valve 654. T pressurebelow its maximum value delays lockup clutch apply by requiring a higherG1 pressure (higher converter turbine speed) to move the lockup valveelement 658 to its apply position. T pressure at its maximum valuepercent travel of the primary TV valve element 587 with engine throttleopen through detent) prevents movement of the lockup valve element 658to its apply position when it is in its release position and forcesmovement of the lockup valve element to its release position when it isin its apply position.

The lockup valve 658 in its apply position connects the main line 510between lands b and c to the lockup clutch line 668 to engage the lockupclutch 238 and also to-urge the main pressure regulator valve element520 leftward to allow more fluid to flow into the lubrication line 546,such added regulator valve bias effecting a reduction in main pressurewhich is permissible because lower torque at higher rotating speeds isbeing transmitted by the power train under these conditions. The lockupvalve 658 in its apply position also connects the converter signal line672 between lands a and b to an exhaust 682 so that the converterpressure regulator valve 442 regulates at the low value which ispossible since with the lockup clutch applied, there is no heat beinggenerated in the torque converter.

FORWARD AND REVERSE SHIFT VALVE The forward and reverse main line 566 inaddition to directing forward and reverse main pressure to the two TVvalves 580 and 582, also directs this pressure to a forward and reverseshift valve 684 shown in FIG. 22. The forward and reverse shift valve684 is for connecting the forward and reverse main line 566 to either aforward clutch line 686 which delivers the pressure to a motor 688operating the forward drive clutch 246 or to a reverse clutch line 690which delivers the pressure to a motor 692 operating the reverse driveclutch 252. The forward and reverse shift valve 684 has a valve element694 having lands a, b c and d of equal diameter located in a bore 696 inthe valve body. The shift valve element 694 is mechanically detented bydiametrically opposed spring loaded balls 698 which engage with eitherone of a pair of concave surfaces between lands c and d to hold theshift valve element in either its reverse clutch apply position as shownor its forward clutch apply position.

In the reverse clutch apply position the forward and reverse main line566 is connected between lands b and c to the reverse clutch line 690 toapply the reverse drive clutch 252. At the same time, the forward clutchline 686 is connected between lands a and b to the lubrication line 546which receives the overage from the main pressure regulator valve 518.The pressure in lubrication line 546 is regulated by a lubricationpressure regulator valve 700 shown in FIG. 2c which has a valve element702 normally biased to the closed position shown by a regulator spring704. Pressure in the lubrication line 546 is maintained by regulatingaction of valve 700 which opens against the spring bias to permit allfluid in excess of that required to maintain lubrication pressure andflow to return to the reservoir via exhaust 706. The regulatedlubrication pressure in the lubrication line 546 is low enough so thatthe fluid at this pressure fills the forward clutch motor 688 but doesnot effect forward clutch engagement to thus ready the disengagedforward drive clutch for subsequent engagement.

When the forward and reverse shift valve element 694 is moved to theright to the forward clutch apply position through the mechanicaldetent, the forward and reverse main line 566 is connected between landsa and b to the forward clutch line 686 to apply the forward drive clutch246. The reverse clutch line 690 is then connected between the-lands band c to the low pressure lubrication line 546 to release the reversedrive clutch 252 while the reverse clutch line 690 and reverse clutchmotor 692 are maintained full of fluid at the low lubrication pressurein readiness for subsequent reverse drive clutch engagement.

The positioning of the forward and reverse shift valve element 694 iscontrolled by fluid pressure bias. The valve bore 696 is closed at bothends providing chambers 710 and 712 at the opposite ends of the valveelement 694. Chambers 710 and 712 are simultaneously supplied with fluidfrom the forward and reverse main line 566 via orifices 713 and 714,respectively, as subsequently described and their closure and exhaust isselectively provided by solenoid valves 715 and 716, respectively. Thechambers 710 and 712 are connected to control lines 718 and 720,respectively, and both of the solenoid valves 715 and 716 are normallyde-energized in which condition they are closed and block the controllines 718 and 720 from exhausts 722 and 723, respectively, to thus closethe chambers. The chambers 710 and 712 when supplied from the forwardand reverse main line 566 then have full forward and reverse mainpressure which acts on the full end area of lands a and d and thus thereis a fluid pressure balance on the valve element 694 and the mechanicaldetent 698 holds the valve in one of its two positions. The solenoidvalves 715 and 716 have internal orifices larger than the orifices 713and 714 and upon energization of one of the solenoid valves it will beopened and exhaust one chamber of pressure through its internal orificepermitting the retained pressure on the other end of the forward andreverse shift valve element 694 to move the valve through the mechanicaldetent into the other detented position. With the forward and reverseshift valve 684 in the reverse clutch apply position shown, energizationof the solenoid valve 716 exhausts chamber 712 of pressure permittingthe retained pressure acting in chamber 710 to move the valve rightwardthrough the detent to the forward clutch apply position. Alternatively,energization of the solenoid valve 715 exhausts chamber 710 permittingthe retained pressure in chamber 712 to move the valve leftward to thereverse clutch apply position.

FORWARD AND REVERSE SHIFT INHIBITOR VALVE A forward and reverse shiftinhibitor valve 724 shown in FIG. 2e permits the forward and reverseshift valve 684 to shift the power train between forward and reverse inthe first drive range and prevents shifting between forward and reversein all higher drive ranges. The forward and reverse shift inhibitorvalve 724 has a valve element 726 with lands a and b of equal diameterlocated in a bore 728 in the valve body. The valve 724 further has a G2plug 730 and a stop plug 732 both of the same diameter as lands a and blocated in the bore 728. A spring 734 normally biases the valve membersleftward to the position shown with plug 732 acting as a stop. In thisposition which is the forward-reverse shift permit position the forwardand reverse main line 566 is connected through the valve 724 between itslands a and b and then through the orifices 713 and 714 to therespective chambers 710 and 712 of the forward and reverse shift valve684. Thus, with the forward and reverse shift inhibitor valve 724 in itsforward-reverse shift permit position, the forward and reverse shiftvalve 684 may be operated by its solenoid valves 715 and 716 toselectively apply the forward drive clutch 246 and the reverse clutch252.

Forward-reverse shift prevention is provided by connecting the G2 line577 to deliver G2 pressure to a chamber 736 where it acts on the fullleft end area of the G2 plug 730 to urge the G2 plug and valve element726 rightward against the spring bias to an inhibit position in whichland a of the valve element blocks the forward and reverse main line 566at the upstream side of the valve and connects the forward and reversemain line 566 at the downstream. sideto an exhaust 740. With bothchambers 710 and 712 of the forward and reverse shift valve 684 thusexhausted by the forward and reverse shift inhibitor valve 724,operation of the solenoid valves 715 and 716 is ineffective to shift theforward and reverse shift valve 684 from the position it then occupieswhich will either be forward or reverse. Since G2 pressure isproportional to the range unit output speed which is zero throughout thefirst drive range, no G2 pressure is delivered to the forward andreverse shift inhibitor valve 684 during first drive range operation ineither forward or reverse and thus the forward and reverse shiftinhibitor valve will be in its permit position as shown to permit theoperator to shift the power train between forward and reverse in thefirst drive range. Exhausts 740, 742 and 744 are provided to preventhydraulic lock in the forward and reverse shift inhibitor valve 724.

When the vehicle is moving in either the forward or reverse direction ineither the second, third or fourth drive range the G2 pressure is alwayspresent and conditions the forward and reverse shift inhibitor valve 724in its inhibit position to prevent the forward and reverse shift valve684 from effecting shifts between forward and reverse. Thus, theoperator is prevented from making a shift between forward and reverse inthe second, third and fourth drive range which might overload the powertrain, shifts between forward and reverse in the first drive range beingpermitted for rocking the vehicle in low traction situations.

SEQUENCE VALVE A sequence valve 746 shown in FIG. 2e is for disengagingthe low low brake 318 during shifts between the first forward and firstreverse drive range to permit engagement of the directional clutches(clutches 246 and 252) under no load conditions recalling thatdirectional changes are prevented in the second, third and fourth driverange in forward and reverse by the forward and reverse shift inhibitorvalve 724. The sequence valve 746 has a valve element 748 having lands aand b of equal diameter and a plug 750 of the same diameter located in abore 752 in the valve body. The valve elements 748 and 750 are biasedrightward by a spring 754 to the position shown which is the releaseposition. In the release position, a 1-2 line 756 which normallyconnects the range line 626 to engage the low low brake 318 as describedin more detail later is connected between the lands a and b of valveelement 748 to an exhaust 758 to release the low low brake 318.

The forward clutch line 686 and reverse clutch line 680 from the forwardand reverse shift valve 684 are continuously connected to the bore 752of the sequence valve 746 at the right end of plug 750 and between valveelement 748 and plug 750, respectively. Thus, when the reverse driveclutch 252 is engaged with the forward and reverse shift valve 684 inthe reverse clutch apply position shown, forward and reverse mainpressure acts on both the full right end area of land b of the valveelement 748 and the full left end area of plug 750 while the lowerlubrication pressure acts on the full right end area of valve plug 750.The fluid pressure imbalance on plug 750 holds it in the position shownand the fluid pressure on valve element 748 moves it leftward againstthe spring bias to 21 normal apply position. In the normal applyposition, land b of valve element 748 blocks exhaust 758 and the 1-2line 756 is connected through the valve between lands a and b for mainpressure transmittal to engage the low low brake 318. When the forwardand reverse shift valve 684 is operated to change vehicle direction fromreverse to forward in the first drive range which normally has the lowlow brake 318 engaged, the forward clutch line 686 is supplied withfluid from the forward and reverse main line 566 which fluid is alsoadmitted to act on the right end of plug 750 while the reverse clutchline 690 is filled with lubrication fluid which is also admitted to acton the right end of land I; and on the left end of plug 750. As theforward clutch 246 is engaged and with the leftward acting fluidpressure on the valve element 748 thus reduced to the low lubricationpressure, the leftward acting pressure on plug 750 is below the normalforward and reverse main pressure because of the flow requirements forthe clutch engagement. This permits the spring 754 to move the valveelement 748 rightward to its release position against plug 750 whichremains to the right so that while the forward drive clutch 246 is beingengaged, the l-2 line 756 is exhausted through exhaust 758 to drop outor release the low low brake 318. The pressure in the forward clutchline 686 rises with engagement of the forward drive clutch until fullforward and reverse main pressure is reached. Full forward and reversemain pressure or a slightly lower pressure is effective to move plug 750and the contacting valve element 748 leftward to reestablish connectionof the l-2 line 756 through the valve and thus reestablish engagement ofthe low low brake 318.

When the forward and reverse shift valve 684 is operated to changevehicle direction from forward to reverse in the first drive range, thefluid from the forward and reverse main line 566 is admitted to act onthe right end of land b of valve element 748 and the left end of plug750 while lubrication fluid is admitted to act on the right end of plug758. As the reverse drive clutch 252 is engaged and with the leftwardacting pressure on the plug 750 thus reduced to the low lubricationpressure, the fluid pressure acting leftward on the valve element 748and rightward on the plug 750 is below the normal forward and reversemain pressure because of the flow requirements for the clutchengagement. This permits the spring 754 to move the valve element 748and contacting plug 750 rightward to the release position so that whilethe reverse drive clutch 252 is being engaged, the low low brake 318 isreleased. The pressure in the reverse clutch line 690 rises withengagement of the reverse drive clutch until full forward and reversemain pressure is reached. Full forward and reverse main pressure or aslightly lower pressure is effective to move valve element 748 leftwardto its apply position to reestablish engagement of the low low brake 318while the plug 750 is held to the right by its pressure imbalance.

NEUTRAL SHIFT VALVE A neutral shift valve 759 shown in FIG. 2b if forconditioning the power train in neutral and has a valve element 760having lands a and b of equal diameter located in a bore 762 in thevalve body. A spring 764 urges the valve element 760 toward the neutralposition shown in which land 0 blocks the range main line 626 upstreamof the valve and connects the range main line downstream of the valvebetween the lands a and b to an exhaust 768. The forward and reversemain line 566 is connected through an orifice 770 to a chamber 772 atthe right end of the valve element 760. A solenoid valve 774 isconnected by a control line 776 to the chamber 772 and when de-energizedblocks the line 776 and thus chamber 772 from an exhaust 778. When thechamber 772 is thus blocked, the chamber is filled through orifice 770and the pressure rises to full forward and reverse main pressure. Thispressure acts on the full end area of land b and is effective to movethe valve element 760 leftward to a range shift position. The valveelement 760 in the range shift position connects the range main line 626through the valve between lands a and 12 while land b blocks exhaust768, an exhaust 779 preventing hydraulic lock in the valve.

When the solenoid valve 774 is energized it connects the chamber 772 viathe line 776 to the exhaust 778 through an internal orifice larger thanorifice 770 to prevent pressure buildup in the chamber which is beingcontinuously fed through orifice 770. This pressure exhaust permits thespring 764 to move the valve element 760 to its neutral positionblocking the range main line 626 at the upstream side and exhausting thedownstream range main line.

MANUAL SIGNAL VALVE A manual signal valve 780 shown in FIG. 2b providesselective delivery of forward and reverse main pressure for manuallycontrolled shifts to all the drive ranges below the highest l, 2 and 3)and T pressure for all automatic shifts. The manual signal valve 780 hasa valve element 782 having lands a, b and c of equal diameter located inportion 784 of a stepped bore 785 in the valve body and a land d ofsmaller diameter located in bore portion 788. A spring 790 biases thevalve element 782 rightward toward the manual signal position shown. Inthis position, the T line 604 is blocked at the upstream side of thevalve by land a and is connected at the downstream side of the valvebetween the lands a and b to an exhaust 789. In addition, the forwardand

1. In a control system for a power train the combination of a pluralityof fluid pressure operated drive engaging means each operable on fluidpressure delivery thereto to establish a drive range; a fluid pressuresource; shift means responsive to torque demand and output speed forselectively establishing fluid pressure delivery from said fluidpressure source to said drive engaging means to automatically shiftdrive ranges in accordance with torque demanD and output speed; steercontrol means for providing a steering operation and a steer signalindicating the occurrence thereof; and automatic shift inhibitor meansresponsive to said steer signal for inhibiting automatic range shiftingduring said steering operation.
 2. In a control system for a power trainthe combination of a plurality of fluid pressure operated drive engagingmeans each operable on fluid pressure delivery thereto to establish adrive range; a fluid pressure source; shift means responsive to torquedemand and output speed for selectively establishing fluid pressuredelivery from said fluid pressure source to said drive engaging means toautomatically shift drive ranges in accordance with torque demand andoutput speed; automatic shift inhibitor means conditionable to inhibitautomatic range shifting by said shift means; variable ratio hydrostaticdrive means for providing a variable drive ratio controlled by controlpressure delivery thereto to produce a steering operation; controlpressure regulator valve means operatively connected to said fluidpressure source for providing a control pressure; steer valve means forcontrolling the delivery of said control pressure to said hydrostaticdrive means to both vary the drive ratio and condition said automaticshift inhibitor means to prevent automatic range shifting duringsteering operation.
 3. In a control system for a power train providingmultiple drive ranges and steering operation the combination of rangeshift means for shifting drive ranges; automatic shift control meansresponsive to torque demand and output speed for controlling said rangeshift means to automatically shift drive ranges in accordance withtorque demand and output speed; manual shift control means includingpower source means for controlling said range shift means to manuallyselect the drive ranges using power from said power source means andreleasing control over said range shift means to said automatic shiftcontrol means on discontinuance of power from said power source means;steer control means for controlling the steering operation and providinga steer signal indicating the occurrence thereof; and said automaticshift control means including automatic shift inhibitor means responsiveto said steer signal for inhibiting automatic range shifting duringsteering operation.
 4. In a control system for a power train thecombination of a plurality of fluid pressure operated drive engagingmeans each operable on fluid pressure delivery thereto to establish adrive range; a fluid pressure source; primary throttle pressureregulator valve means operatively connected to said fluid pressuresource for providing a TV pressure increasing with increasing torquedemand and a T pressure equivalent to and derived from said TV pressureabove a predetermined intermediate TV pressure; secondary throttlepressure regulator valve means operatively connected to said fluidpressure source and said primary throttle pressure regulator valve meansfor providing a range TV pressure having a predetermined minimum valuegreater than zero and otherwise equivalent to and derived from said TVpressure; first governor means for providing a G1 pressure increasingwith increasing output speed; second governor means for providing a G2pressure having a value of zero throughout the lowest drive range andincreasing with increasing output speed throughout the higher driveranges; shift valve means corresponding to each of said drive engagingmeans; said shift valve means operatively connected to theircorresponding drive engaging means and operatively connected in seriesto said fluid pressure source; the furthest downstream shift valve meansoperable in a downshift position to establish fluid pressure deliveryfrom said fluid pressure source to the drive engaging means thatestablishes the lowest drive range and in an upshift position to exhaustfluid pressure from the last mentioned drive engaging means whileestablishing Delivery of the fluid pressure to the drive engaging meansthat establishes the next higher drive range; each of the other of saidshift valve means operable in a downshift position to establish fluidpressure delivery from said fluid pressure source to the immediatedownstream shift valve means and in an upshift position to exhaust fluidpressure from the immediate downstream shift valve means whileestablishing delivery of the fluid pressure to the corresponding driveengaging means; means transmitting said G1 pressure to act on saidfurthest downstream shift valve means for providing an upshift biasbiasing said furthest downstream shift valve means to its upshiftposition; means transmitting said G2 pressure to act on all of the otherof said shift valve means for providing an upshift bias biasing each ofthe other of said shift valve means to its upshift position; meansnormally transmitting said range TV pressure to act on each of saidshift valve means only when each said shift valve means is in itsdownshift position for providing an upshift inhibitor bias opposing saidupshift bias on each said shift valve means; means normally transmittingsaid T pressure to act on each of said shift valve means for providing adownshift bias biasing each of said shift valve means to its downshiftposition; manually controlled signal valve means for preventing said Tpressure from acting on all of said shift valve means while transmittinga pressure derived from said fluid pressure source to act on all of saidshift valve means for providing a constant downshift bias biasing eachof said shift valve means to its downshift position; manually controlledshift controlling means corresponding to and operatively connected toeach of said shift valve means for selectively providing an upshift biason each of said corresponding shift valve means effective to immediatelybias the corresponding shift valve means to its upshift position; andsignal operated automatic shift inhibitor valve means for preventingtransmittal of said T pressure to all of said shift valve means andtransmitting a pressure derived from said fluid pressure source insteadof range TV pressure to all of said shift valve means to provide aconstant upshift inhibitor bias to hold each of said shift valve meansin its downshift position.
 5. The control system set forth in claim 4and a steer control system for the power train, said steer controlsystem having signal means for transmitting a signal to operate saidautomatic shift inhibitor valve means during steer control.